Randomized benchmarking with gate-dependent noise

We analyze randomized benchmarking for arbitrary gate-dependent noise and prove that the exact impact of gate-dependent noise can be described by a single perturbation term that decays exponentially with the sequence length. That is, the exact behavior of randomized benchmarking under general gate-dependent noise converges exponentially to a true exponential decay of exactly the same form as that predicted by previous analysis for gate-independent noise. Moreover, we show that the operational meaning of the decay parameter for gate-dependent noise is essentially unchanged, that is, we show that it quantifies the average fidelity of the noise between ideal gates. We numerically demonstrate that our analysis is valid for strongly gate-dependent noise models. We also show why alternative analyses do not provide a rigorous justification for the empirical success of randomized benchmarking with gate-dependent noise.Comment: It measures what you expect. Comments welcome. v2: removed an inconsistent assumption from theorem 3 and clarified discussion of prior work. Results unchanged. v3: further clarified discussion of prior work, numerics now available at https://github.com/jjwallman/numerics. v4: licence change as required by Quantu

Network Capital and Social Trust: Pre-Conditions for ‘Good’ Diversity?

This paper unpicks the assumption that because social networks underpin social capital, they directly create it – more of one inevitably making more of the other. If it were that simple, the sheer quantity of networks criss-crossing a defined urban space would be a proxy measure for the local stock of social capital. Of course the interrelationships are more complex. Two kinds of complication stand out. The first is specific: networks have both quantitative and qualitative dimensions, but the two elements have no necessary bearing on each other. The shape and extent of a network says nothing about the content of the links between its nodes. Certainly the line we draw between any two of them indicates contact and potential connection, but what kind of contact, how often, how trusting, in what circumstances, to what end…? Reliable answers to these questions need more than surface maps or bird’s eye accounts of who goes where, who speaks to whom. The second complication is a general, not to say universal, difficulty. We are stuck with the fact that sociological concepts - networks, social capital and trust included - are ‘only’ abstractions. They are ways of thinking about the apparent chaos of people behaving all over the place – here, to make it worse, in multi-cultural urban environments - but none of them is visible to be measured, weighed or quantified. This does not make the concepts ‘untrue’, and it should not stop them being useful. My hope is that we can find a nuanced perspective which will at least make the complications intelligible. At best, a multi-layered model will account for diversity in the nature of trust; and for variations in the way social capital is hoarded or distributed within and across ethnic boundaries. It would be contribution enough if we were able to specify the conditions which cause social capital, as Puttnam formulates it, to be exclusionary or inclusionary in its effect.Network capital, Social trust, ‘Good’ diversity

The Diversity of Diversity: Implications of the Form and Process of Localised Urban Systems

This paper summarises research into localised urban systems which accounts for variations in styles of diversity within multi-cultural cities. New work builds on previous studies in London and Turin. The first produced an ideal type model of open:closed urban systems and evidence that the former have better capacity to incorporate incomers. The second revealed the need to adapt the model to account also for the process of diversity. This third phase combines ethnography with computer simulations to reveal emergent properties as well as present styles of urban systems, and to rank the variables driving change. The outcome will be a typology for users dealing with migrant settlement and urban regeneration.Typology of urban systems, Diversity, Relatedness, Process models, Ideal types

Where Have All The Young Men Gone? Evidences and Explanations of Changing Age: Sex Ratios in Kampala

In the second half of the twentieth century the population of Kampala grew substantially and the long-remarked surplus of men over women began to level out. These general trends are equally evident in other African cities, but important differences show up when the balance of age cohorts within the male and female populations is considered. Thus in Kampala, along with population growth and a declining overall sex ratio, censuses show a growing excess of girls/young women over boys/young men. The article reviews these population data and two levels of (unenumerated) explanation for them. The first is extrapolated from Uganda's recent history; the second from observation and narrative in one densely populated parish. The argument is that changes in the age–sex ratio follow from change in the map of work options in Kampala. The disappearance of young males stems from the collapse of the formal economy, once the employer of men, and the developments in the informal economy which favour young women. This conclusion is supported by census data from Nairobi, where the formal employment structure remains relatively buoyant, and the comparable age–sex ratios are less extreme. The health policy relevance of the Kampala trend is underlined by official calculations of increasing HIV/AIDS incidence among teenage women. As long as sex work remains dominant among their options in the informal economy, one effect of their economic advantage is extra vulnerability to fatal disease

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Agricultural and Food Policy, Environmental Economics and Policy, Farm Management, Land Economics/Use, Production Economics,